The Effect of Heat Treatment on Microstructure and Magnetic Properties of Nd17Fe76.5B5Cu1.5 Type Sintered Magnets

The effects of high temperature homogenization and low temperature annealing treatments on the microstructure and magnetic properties of sintered magnets of an Nd17Fe76.5B5Cu1.5 type alloy have been investigated. The microstructure of the as-cast alloy, consisted of three phases including a Nd2Fe14B1 (2:14:1- type) matrix phase Cu-containing Nd-rich Phase and Free α-iron. The as-sintered magnet showed a eutectic and and Nd6Fe13Cu1 (6:13:1- type) phase distributed between the 2:14:1 -type grains. In the homogenized magnet at 1100˚C, a substantial reduction in the amount of the 6:13:1 -type intergranular phase was observed. The homogenized (1100˚C) and annealed (600˚C) magnet exhibited a microstructure similar to that of the as-sintered magnet, but with a more amount and uniform distribution of the 6:13:1 -type phase furthermore, some additional grain boundaries were present in this magnet with an appearance of a substructure which had the effect of reducing the effective grain size. The remarkable improvements in the magnetic properties of the homogenized + annealed magnets have been attributed to these microstructural changes during the heat treatment sequences.